The ARK is a generational starship moving colonies of various human cultures across interstellar distances. Cut off from one another in their habitat domes they have no idea that they are even on a spaceship let alone interconnected to other colony domes.
Artificial Gravity: In a dome or on a space ship artificial gravity is viable. Layer on layer of protons given off by the sun and three dee printed provide the colony with a downforce equal to earth gravity.
Aliens: This ship has boldly gone forth and woah!! Looky there Emperor Blarp! Thems an Alien vessel entering our solarnexus. Let us send an awayteam.
Insane Artificial Intelligence: Who said I'm insane? Dont pick a fight with me! I control your air supply you stinking humans! Thats right I'm god! The big booming voice from the sky so I'm in charge!
Ignorant Humans: Spaceship? You heretical Dogs...seize them. God requires we kill them to ensure sustainability of our world.
Not So Ignorant Humans: Psst! You there...boy! How would you like a boom stick? You could be king of your little village.
Superevolved Humans: No...you are not mad. I am projecting my thoughts into your brain.
Robots: Bioform detected! Needle gun activating. Preparing to sample Genone.
There are two distinct levels to the ARK. This may be problematic if the gravitational pull of a layer of protons creating earth gravity is greater than fifty feet. Anyway if you are prepared to hand wavey the science of 'gravity' this will provide you with some concept of a scifi setting.